Aquariums and water gardens have long been known as habitats for aquatic life. The presence of these miniature aquatic environments is often used as a way to enhance the environment in which they are placed. In addition to their decorative role, aquariums and water gardens also act as sanctuaries and instructional tools in the observation of aquatic ecology.
Fish bridges, swimways or other types of aquarium extensions employing a partial vacuum to hold a volume of water above the surface of an aquarium are known. These extensions provide aquarium enthusiasts with the means to expand the habitat available to their aquatic animals and may also be used as a water-filled link two or more separate aquaria. Once in place these aquarium extensions use a partial vacuum to defy the water line, retaining a given volume of water indefinitely. As long as the entrance to the bridge or swimway remains below the surface of the water in the underlying aquarium, and the extension maintains the integrity of the partial vacuum, there is no change in the water level inside the aquarium extension.
Examples of bridge assemblies and other aquarium extensions are disclosed in U.S. Pat. No. 5,447,123 (Hendrickson); U.S. Pat. No. 3,991,715 (Gibson Jr.); and U.S. Pat. No. 1,943,417 (Bringman). While these patents disclose the concept of an aquarium extension above the surface of an aquarium, none of them offer a method by which the water level inside the extension attachments is quickly and easily controlled by a user. As exemplified by the above patents, the prior art discloses only manual methods for changing the water volume in an extension attachment, typically involving the manual elimination of the vacuum by the user, after which the entire extension attachment must be submerged in the underlying aquarium or other body of water to regain the partial vacuum. Due to the necessity of manually filling or emptying an extension, the resulting size and number of extensions used is limited, thereby curtailing applications of aquarium extensions in anything other than small home aquariums.
In addition, existing aquarium extensions make no effort to attract aquatic life directly into the extension structure where they are easily observed by people. Instead, existing aquarium extensions rely on the animals to move into or through the structure by chance, limiting use of the extended habitat as a primary observation platform.